[Slartie]

> Today solar panels make sense in terms of money ROI but not in terms of KWh ROI

That is clearly wrong. Even the worst-case embodied energy assumptions for solar panels estimate the cost of producing a square meter of solar panel area at 2000 kWh (the best cases are around 300, see https://en.wikipedia.org/wiki/Energy_return_on_investment#Ph... ). A square meter of solar panel area produces an average of 200 kWh of power per year in Germany (which implies a pessimistic assumption, more sunnier countries can get a multiple of that). This means that even in the worst case, the solar panel has amortized itself from the perspective of embodied energy after 10 years. On average it will be more like below 5 years. Solar panels however have an expected lifetime of well over 30 years and require no maintenance if installed correctly.

[alexey-salmin]

30 years lifetime (if there are no heavy storms), 5-10 years to recoup energy, that's 3-6 EROI. Then you also need to include inverters which are energy-heavy. If we're talking of any meaningful scale, then you also need to include batteries because without them panels get shut down during sunny hours lowering the EROI even further.

In the end you're lucky if you get EROI of 1.5-3. That's an extremely bad deal. All other sources of energy, renewable or not, are in the 20-100 territory. The purpose of the energy production system is not to barely sustain itself but to actually produce usable electricity for everything else you want to do. It's the means, not the ends.

Solar panels have very solid benefits of course, you can buy them for your house to be more autonomous -- I would do that if I had a house. But from the energy/CO2 perspective what you're doing is buying a sort of "battery" that was charged with cheap coal-based electricity in China and shipped off to US/Europe. This makes sense in certain situations but presenting this as a green solution or as future of humanity is just delusional.

[Slartie]

> Then you also need to include inverters which are energy-heavy.

Scientific publications say otherwise. It's quite hard to come by any numbers, but page 11 of https://www.wisdomlib.org/uploads/journals/mdpi-sust/2025-vo... says that typical solar inverters require about 15 MJ/kW of power for their production in total, which would amount to approx. 4 kWh per kW of inverter power. A solar panel square meter produces about 200-250 watts of peak power, so it needs inverter power that cost about 1 kWh to build. Let's triple that, because inverters have a typical lifetime of 10 years in contrast to the 30 years of solar panels. 3 kWh for the inverter is negligible when compared with 300-2000 kWh for the panel itself. So we can just ignore that.

Batteries are interesting. According to https://www.mdpi.com/2076-3298/12/1/24, it takes about 35 kWh in total to produce 1 kWh of battery capacity. Let's say we'll need 250 Wh of capacity for our 250 WPeak solar panel square meter (the rule of 1 kWh capacity for each 1 kWp is a typical estimate applied when sizing solar installations for residential homes). That makes up about 8 or 9 kWh to produce this battery capacity. Admittedly that doesn't include the raw materials, of which the cell requires quite a few expensive ones. Unfortunately I wasn't able to find a good resource on that, so I resorted to asking ChatGPT for a rough calculation, and it came up with about 140 kWh for our 250 Wh LFP cell, which doesn't sound entirely wrong, as it assumed a cell weight of 1,5 kg and splitted that up into different materials. The weight matches what I would expect from personal experience with LFP batteries.

Basically, we can just ignore the inverter and must add about 150 kWh for the battery to our 300-2000 kWh for the panel. That does not substantially impact an EROI calculated from a 1000 kWh assumption for the panel alone.

And this is a calculation based on Germany. Again: weather conditions are far from optimal for solar in Germany. It's much better in many regions in China, where solar panels are made. They can easily achieve EROIs of 20+ with solar there, which is probably the reason why China installs absolutely HUGE numbers of panels. But according to you, they must be "delusional" over there.

[alexey-salmin]

> > This makes sense in certain situations but presenting this as a green solution or as future of humanity is just delusional.

> which is probably the reason why China installs absolutely HUGE numbers of panels. But according to you, they must be "delusional" over there.

State-run economies get delusional pretty easily, but in this case China is safely on the "makes sense in certain situations" side:

* keep electricity prices low

* invest heavily in nuclear

* install solar within reasonable limits (currently around 8% of the grid)

* for better or for worse they burn more and more coal every year

They certainly don't make insane green commitments and they don't say solar is the future of humanity. I don't like China much, but I don't see how they can fall into "delusional" category according to my criteria above, they have none of it.

Now Germany's policy is the complete opposite of China's, except for the "burning coal" part. Germany killed their own economy over high electricity prices because they wanted to go green, but then somehow they've got almost 2x CO2 emissions per capita compared to France.

If someone says "I sacrifice A to get B", but then never get the B and still lose A, and then insist that the plan was a great success -- he's certainly delusional, that's like the definition of the word.